1. Field of the Invention
The present invention relates to a digital cordless telephone set and, more particularly, to a digital cordless telephone set capable of simultaneously waiting for a radio wave from a radio base station connected to a public line and a radio wave from a master unit connected from a private line and automatically controlling incoming call wait periods for the respective radio waves.
2. Description of the Prior Art
Conventionally, a cordless telephone set of this type, e.g., a cordless telephone set disclosed in Japanese Unexamined Patent Publication No. 8-237746 shown in FIG. 1 has a control section 23 which automatically selects connection of a subsidiary unit 21 to a radio base station or a master unit depending on whether the subsidiary unit 21 is placed on a charging unit 22. Upon detecting that the subsidiary unit 21 is placed on the charging unit 22, the line to be connected to the subsidiary unit 21 is set to a private line: otherwise, a public line is set as the line to be connected to the subsidiary unit 21, thereby performing switching control.
Additionally, as disclosed in Japanese Unexamined Patent Publication No. 8-172666, in an area where a radio wave from the radio base station of the private system can be received, the telephone set waits for a ringing signal from the radio base station of the private system. In an area where a radio wave from the radio base station of the public system can be received, the telephone set waits for a ringing signal from the radio base station of the public system. In an area where the radio waves from the radio base stations of both the public and private systems can be received, the telephone set waits for ringing signals from both the public and private systems.
In these prior arts, on the basis of whether the subsidiary unit is within the area where the radio wave from the radio base station connected to the public line or the radio base station (to be referred to as a master unit hereinafter) connected to the private line can be received or whether the subsidiary unit is placed on the charger, the telephone set determines to wait for the radio wave from the radio base station connected to the public line, the radio wave from the master unit connected to the private line, or the radio waves from both systems.
However, when the telephone set is to wait for both the radio wave from the radio base station connected to the public line and that from the master unit connected to the private line, the current consumption during the wait state is higher than that during which the telephone set is waiting for only one of the radio waves, so the continuous waitable time is shortened.
This is because the wait operation for the radio wave from the radio base station connected to the public line and the wait operation for the radio wave from the master unit connected to the private line are simply simultaneously performed (FIG. 2). Reference symbol Wt in FIG. 2 represents the period for waiting for the radio wave.